Coatings that contain a volatile component, such as water and/or an organic solvent, undergo a decrease in volume as the volatile component evaporates from the surface of the coating. As the volatile component leaves the coating, contraction forces act to pull the coating inward in all directions. Without intending to be bound by any particular theory, it is believed that if the coating has sufficient cohesive strength, the coating will contract in only one dimension in a manner such that the coating thickness will decrease while the coating resists contraction in any direction parallel to the substrate surface. In contrast, if a coating lacks cohesive strength sufficient to resist contraction parallel to the substrate surface, contraction forces will cause the coating to break up into small flat segments that are separated by gaps or continuous linear voids. This surface defect is commonly referred to as “mudcracking.”
Precut asphalt- or rubber-based patches can be used for lining floor pans, deck lids and doors of automobiles to dampen or reduce road and engine noise and vibrations, preventing them from permeating into the passenger compartment of the motor vehicle. Sprayable coatings which are capable of being applied by robotics are desirable to provide for labor and cost savings, and flexibility in design specifications for imparting desired sound and vibration damping properties.
Exposure of coatings to water can cause damage to the coating and water absorption may increase coating weight, soften the coating, and/or reduce damping.